Ringing arrangement for carrier circuits



June 22 1926.

O. H. LOYNES ET AL RINGING ARRANGEMENT FOR CARRIER CIRCUITS Filed April 1, 1924 sult that it becomes Patented June 22, 1926.

UNITED STATES OWEN H. LOYNES, 01'. BROOKLYN,

OBS TO AMERICAN TELEPHONE AND OF NEW YORK.

amcme aaaanonunur Application filed April 1,

This invention relates to signaling circuits and more particularly to arrangements for transmitting ringing signals .over multiplex carrier circuits. d

In multiplex carrier circuits of the type in which the carrier is suppressed at the transmitting station,difiiculty has been encountered in transmitting ringing signals, for the reason that the filters in such cir- 10 cuits are usually designed so as to cause a high attenuation to the carrier current but under this condition the filters also cause a rather high transmission loss to frequencies near the carrier frequency, with the redifiicult to transmit a side band obtained by modulating the carrier current in accordance with the usual ringing current of cycles or 135 cycles.

In accordance with the present invention 20 this difiiculty is overcome by so arranging the circuit that an intermediate carrier current, having a frequency of, say, a thousand cycles and lying well within the voice range, is modulated by a ringing frequency of, say, 135 cycles. The modulated intermediate carrier is then impressed upon the modulator to modulate the normal carrier assigned to that channel.- One of the side bands resulting from the last step of modulation will then be freely transmitted through the filter and will carry com onents corresponding to the ringing requency which may be detected at the receiving station.

The invention will now be more fully understood from the detailed description thereof when read in connection with the accompanying drawing, the figure of which illustrates a circuit diagram embodying a preferred form of the invention. Referring to the drawing, L designates a low frequency transmission line associated with the transmitting channel TL and a receiving channel BL of the carrier system through the usual hybrid coil 10. The line L is balanced by a network N so that the transmitting channel TL and receiving channel RL will be substantiall conjugate with respect 5 to each other. T e transmitting channel TL includes the usual type of balanced modulator M, comprising vacuum tubes VT and VT. An oscillator O is associated with the balanced input circuit of the modulator M through a transformer 11 and thus sup- TELEGRAPH COMPANY, A CORPORATION roa canama cmcurrs.

1924; Serial No. am.

plies the carrier frequency assigned to the channel.

The receiving channel includes the usual balanced demodulator D, comprising vacuum tubes VR and VR'. A suitable source of carrler frequency S is associated with the lnput c1rcu1t of the balanced demodulator D through a transformer 15, the carrier frequency being thus su plied to the receiving channel to take the p ace of the carrier component which is suppressed at the modulator of the transmitting station.

In order that a ringing signal may be transmitted over the channel TL an oscillator O is provided for generating an intermediate carrier current, the frequency of which lies withm the voice range. This source may be of any frequency range well within the voice range and in the case illustrated is assumed to have a frequency of a thousand cycles. A relay 30 is provided which is common to all of the transmitting channels of the multiplex circuit and thisrelay responds whenever a ringing signal comes in over an line, such as L, which 'is multiplexed or transmission over the same carrier circuit. When so energized the relay 30 connects a ringing source, which may be, for example,-of a frequency of 135 cycles, to the plate circuit of the tube 0 to modulate the oscillations generated by said tube 0'. A relay 31 is also provided, this relay being individual to the line L and responsive to a ringing signal incoming from said line. When the relay 31 is energized it connects the oscillator O to the in ut transformer 24 of the modulator M so that the modulated intermediate carrier frequency of 1,000 cycles will be impressed upon the modulator to modulate the normal carrier frequenc impressed upon said modulator by the oscil lator O.

The apparatus for receiving the rin signal comprises a detector D bridged throu h a transformer 32, across the receiving 0 annel RL on the out ut side of'the demodulator D. The dem ulator D, when a ringing signal is received, operates to detect the intermediate frequency of 1,000 cycles modulated. by the rin 'n' frequency. This intermediate modulate Ere none is then impressedupon the detector D, which operates to accordance with which the intermediate AND RUSSELL S. OHL, 0] NEW YORK, N. Y., ABBIGH- detect the cycle frequency in frequency is modulated. An alternating current relay 17 is provided which operates in response to the detected 135 cyc e freqlliency to impress a ringing current upon t e line L.

Further details of the apparatus will be understood from the description of the operation which is as follows: Ringing current incoming from the line L is impressed over the back contacts of rela 20 u 11 an alternating current relay 21.. elay 2 closes "'a; circuit over its front contact through re- .the

lays 13 and 23 in series. Relay 23, upon bein ener' 'zed, disconnects the line L from ybri coil 10. Relay 13, at its inner contacts, disconnects the detector D from the output transformer 28 of the demodulator D and at its outer up r contact disconnects the demodulator D on the hybrid coil 10. At its outer lower contact, relay 13 connects ground to a conductor 33, thereby completin the circuits of rela s 30 and 31 res tive y. Relay 30, u n ing energiz connects a source 0 ringing current having a frequency of 135 cycles, for

' exam Is, to the plate circuit of the oscillator e oscillator O normally generates an intermediate carrier frequency of, say, 1,000 cycles and this frequency is modulated by the 135 cycle source, with the result that frequencies of 1,000 cycles, 1,135 cycles and 865 cycles respectively are impressed upon the output transformer 34 of the oscillator 0'. Relay 31, upon being energized, connects the output transformer 34 to the input transformer 24 of the modulator M so that the three frequencies above referred to are impressed upon the modulator M and modulate the normal carrier frequency su v plied to the modulator from the oscillator ated with the output circuit of the modulator M, is arranged to ass only one side band, say, the upper si e band. Consequently, the lower side band frequencies 8,865 cycles, 9,000 cycles, 9,135 cycles, together with the ori 'nal frequencies of 1,000 cycles, 865 cyc es, and 1,135 cycles will be suppressed by the filter. The upper side band frequencies of 11,135 cycles, 11,000 cycles and 10,865 cycles, it will be observed, fall well within the range of free transmission of the output filter, whose range of free transmission may be, for exam le from 10 cycles to 12,200 cycles. J 200 The receiving operation is as follows: Assuming that requencies of 11,135 cycles, 11,000 cycles and 10,865 cycles are transmitted from the distant station, these frequencies pass through the band filter RF on the input side of the demodulator D and are then impressed upon this demodulator. In the case assumed, a frequency of 10,000 cycles will be sup lied to the demodulator from the source 5 and will beat with the received frequencies so that components of the detected currents will appear in the output circuit of the demodulator corres ndmg to 1,135 cycles, 1,000 cycles an clyl'cles. These three frequencies will pass t rough the transformer 28 and thence through the transformer 32 to the input circuit of the demodulator l), which detects a component correspondin to 135 cycles. Th s component is impresse u on the alternating current relay 17, whic is tuned to 135 cycles. The relay 17, u on being energized, completes circuits f dr the relays 20 and 27. Relay 27 completes a circuit of relay 23, which operates to disconnect the hue L from the hybrid coil 10. Relay 20, on the other hand, connects a rin 'ng source of 20 cycles, for example, to the ins L over the conductors 19 so that ringing current is transmitted to the line L.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely diflerent from those illustrated without departing from the spirit and scope of the appends claims. What is claimed is:

1. The method of transmitting a ringing frequency lower than the ordinary telephone range over a carrier system, in which a carrier frequency is modulated in accordance with speech and the carrier and frequencies in the neighborhod of the carrier are suppressed, which consists in, modulating an intermediate carrier current having a frequency well within the telephone range in accordance with the ringing frequency, and then modulating the normal carrier of the carrier. channel in accordance with the modulated intermediate frequency to produce a side band containing components from which the ringing frequency may be detected.

2. The method of transmitting a ringing frequency lower than the ordinary telephone range over a carrier system in which a carrier frequency is modulated in accordance with speech and the carrier and frequencies in the neighborhood of the carriertelephone range in accordance with the ringing frequency, and modulating the normal carrier frequency of the carrier channel in accordance with the modulated intermediate frequency to produce side bands one of whichlies well within the range of free transmission of the fi1ter.'

3. In a signaling system, a carrier channel including a modulator for modulatin a carrier frequency in accordance wit speech, means associated with said modulator for su pressing the carrier and frequencies int c neighborhood of the carrier, means to generate an intermediate carrier frequency well within the ordina telephone range, means to modulate said carrier frequency in accordance with a ringing frequency below the ordinary telephone range, and means to modulate the normal carrier of the channel infaccordance with the modulated intermediate frequency to produce side bands, at least one of which lies well within the range of free transmission of the channel.

4. In a signaling system, a carrier channel including a modulator for modulating a carrier frequency in accordance with speech, means associated with said circuit for su pressing the carrier and frequencies in t e neighborhood of the carrier, means to generate an intermediate carrier frequency well within the ordinary telephone range, means to modulate said carrier frequeno in accordance with a ringing frequency be ow the ordinary telephone range, means to modulate the normal carrier of the channel in accordance with the modulated intermediate frequency to produce side bands, at least one of which lies well within the range of free transmission of the channel, a demodulator at a receiving station for detecting a component corresponding to the modulated intermediate carrier, means for producin from the detected component the ringing requency, and means responsive to the ringing frequency for transmitting a ringing signal.

5. In a signaling system, a carrier channel, a source of carrier frequenc therefor, a balanced modulator upon whic said carrier frequency may be impressed and modulated in accordance with speech, the circuit of said modulator being so balanced as to substantially prevent the transmission of the modulated com onent corresponding to the carrier, a filter or said channel for su pressing the carrier and frequencies in t e neighborhood of the carrier and for suppressing fre uencies lying within the range of one side and, means for generating an intermediate carrier frequency well within the ordinary telephone range, and means responsive to a ringing frequency below the or inary telephone range to modulate said intermediate carrier frequency in accordance with said ringin frequency and to im ress the modulate current u n said ba anced modulator to produce si e bands, at least one of which is well within the range of free transmission of the filter.

6. In a signaling system, a carrier channel, a source of carrier frequency therefor, a balanced modulator upon whic said carrier frequency may be im ressed and modulated in accordance wit speech, the circuit of said modulator being so balanced as to substantially prevent the transmission of v the modulated com onent corresponding to the carrier, a filter or said. channel for su pressing the carrier and frequencies in t e neighborhood of the carrier and for suppressing fre uencies lying within the range of one side and, means for generating an intermediate carrier frequency well within the ordinary telephone range, means responsive to a ringing frequency below the ordinary telephone range to modulate said intermediate carrier frequency in accordance with said ringing frequency and to imlpress the modulated current upon said ba anced modulator to produce si e bands, at least one of which is well within the range of free transmission of the filter, a demodulator at a receiving station for detecting from the transmitted side band a component corresponding to the modulated intermediate frequency, means to translate said detected component into a ringing frequency, and means responsive to said ringing frequency for transmitting a ringing si al.

our names to t is specification this 31st day n testimon whereof, we have signed. 

